1. Field of the Invention
The present invention relates to a producing method of a high speed FV (force variation) reducing tire in which, for each of rn-number of raw tires in the same lot, a variation amount of a total gage of a tread portion and high speed FV in a completed tire formed by vulcanization-forming the raw tires are measured to obtain a predetermined estimation equation, mounting phases of raw tires after the m-th tire with respect to the vulcanization mold are specified based on the estimation equation, and thereby an n-order component of high speed FV of the completed tires after the m-th tire is reduced.
2. Prior Art
In order to improve vehicle vibration resulting from a tire, it is necessary to reduce a vibration force generated by the tire, and a 100% inspection of low speed uniformity is conventionally carried out in many cases when the tires are produced. A measuring method of the low speed uniformity is laid down in JASOC607-87. According to this method, uniformity factors such as a radial FV, a tangential FV, a lateral FV, and a radial runout (RRO) are measured at low rotation speed of 60 rmp or lower.
In recent years, it has been found that a higher-order component of the high speed uniformity is strongly involved in vibration and noise caused by running at high speed. Therefore, the desire to provide tires having excellent high speed uniformity grows in the tire market. However, since it is necessary to measure the high speed uniformity at high speed rotation using a special uniformity machine, it takes a long time for carrying out the measurement, and it is extremely difficult to carry out the 100% inspection.
Thereupon, in recent years, it has been proposed to estimate the higher-order component of the high speed uniformity of a tire using a regression equation or a statistical processing from a uniformity factor of the low speed uniformity.
FIG. 10(A) shows a relation between high speed radial FV2-order and low speed radial FV2-order. FIG. 10(B) shows a relation between the high speed radial FV2-order and RRO2-order. As shown in these drawings, since the tire uniformities have different mechanisms depending upon speed, a correlation between the low speed uniformity and the high speed uniformity is not high and thus, it is difficult to sufficiently enhance the estimation precision of the higher-order component of the high speed uniformity. In the conventional technique, it is only possible to discriminate a completed tire based on the estimation, and it is not possible to positively produce a tire having excellent high speed uniformity.
In view of such circumstances, the present inventor researched and found the following fact. That is, in the same lot, there were high correlations between magnitude and phase of an n-order component of a total gage distribution of a tread portion in a raw tire, between magnitude and phase of variation of local total gage at a joint position of various tire constituent members in the raw tire (e.g., inner liner rubber, tread rubber, carcass ply, belt ply and the like) in a circumferential direction of each tire, and between magnitude and phase of the high speed FV n-order component in the completed tire obtained by vulcanization-forming the raw tire. Based on the information, the estimation equation was obtained from a leading sample of the same lot, thereby making it possible to precisely estimate, for the tires after the sampled tire, the n-order component of high speed FV when this raw tire became the completed tire in a state in which the tire remained as the raw tire. For the tires after the sampled tire, if the mounting phase of the raw tire to the vulcanization mold was specified based on this estimation, the n-order component of high speed FV of the completed tire could be reduced.